Northern Prairie Wildlife Research Center
Northeast Wetland Flora
Field Office Guide to Plant Species
Alnus rugosa (DuRoi) Spreng.
- Family: Birch (Betulaceae)
- Flowering: March-May
- Field Marks: The distinguishing features of this alder are the conspicuous white lenticels or
the trunk and on the twigs, the short, thick stalks of the "cones," and the conspicuous net
venation of the leaves. In winter the immature female spikes hang down.
- Habitat: Along streams, in swamps.
- Habit: Shrub to 20 feet tall, with dark gray bark speckled with white lenticels.
- Stems: Twigs reddish brown, smooth; buds sessile, pointed, sticky.
- Leaves: Alternate, simple, dark green on the upper surface, paler or sometimes whitish on the lower surface, oval to ovate, rounded or pointed at the tip, rounded or tapering to the base, toothed or doubly toothed, smooth or hairy, conspicuously net-veined, up to 5 inches long, with a stalk up to 1/2 inch long.
- Flowers: Male and female flowers borne separately, but on the same plant, the male flowers 3 in a cluster and subtended by 4-5 bractlets, all in a slender spike up to 2 inches long, the female in a few ovoid spikes up to 3/4 inch long, on short stalks or sessile.
- Sepals: 3-5, minute, green, united to each other.
- Petals: 0.
- Stamens: 3-5.
- Pistils: Ovary inferior.
- Fruits: Many nutlets aggregated into a "cone," with each nutlet subtended by a woody bract, the nutlets narrowly winged, ovoid to nearly spherical, 1/10-1/6 inch long.
- Notes: This species is called A. incana by Gleason and Cronquist. This is a variable species with regard to leaf color, leaf shape, and hairiness.
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